The present invention generally relates to a process for deforming and coating metallic surfaces and, more particularly, to a process for deforming and coating metallic surfaces in association with the manufacture of steel drums and pails.
It is known in the prior art to manufacture steel drums by forming a sheet of steel into cylindrical shape and welding the joint to form a longitudinal seam. In one type of drum, commonly referred to as a "tight-head" drum in the industry, circular top and bottom heads are then cut from another sheet of steel and affixed to the cylindrical shell by means of an operation commonly referred to as "seaming". In the "seaming" operation, lubricated forming rolls are utilized to join the heads to flanges extending from the cylindrical shell in a two-step folding process. In a second type of drum, known in the industry as a "full-removable-head" drum, the bottom head is joined to the cylindrical shell by the "seaming" operation while the top head is secured so as to be fully removable from the shell. Typically, the metal top of the shell is rolled to form a "false wire" or "bead" to which the top head is secured by means of a closing ring. An appropriate gasket may also be provided to insure adequate sealing. Also, prior to the actual "seaming" operation, an appropriate sealing compound may be applied to the bottom head in the case of full-removable-head drum and to both the top and bottom heads for a tight-head drum. The design and construction requirements for both types of drums is fully disclosed in the USA Standard Specification for Metal Drums and Pails, published by the United States of America Standards Institute, which is incorporated herein by reference.
Subsequently, special purpose drum enamels, which provide the desired paint film properties of high gloss, good abrasion and wear resistance, good weathering properties such as fade resistance and gloss retention, and good corrosion resistance, are applied to the exterior of the drum which is then ready for shipment to the user. Frequently, a "baking enamel" which is heat-cured in an oven is used for this purpose.
To best insure the provision of the aforementioned desired properties, prior art drum coatings have typically comprised solvent-based formulations. However, in view of the recently increased emphasis on air pollution control and energy conservation, it would be highly desirable to utilize drum coatings comprising water-borne formulations rather than the solvent-based formulations widely used at the present time. Although substitutions of water-borne drum finishes for the solvent based types have been attempted, these attempts have not produced altogether satisfactory results. The primary impediment to the workable substitution is attributable to the contamination of the metal surface of the drums introduced by the forming lubricants during the "seaming" or other metal forming operations. Although the surface contamination introduced by the lubricants, which are typically petroleum based products, apparently does not interfere with the application of solvent-based coatings to the drums, their presence on the metal drum surface seriously interferes with the integrity of the coatings when the application of a water-borne formulation is attempted. Due primarily to this limitation, the industry has not accepted the use of water-borne drum finishes even though certain highly desirable advantages could be achieved thereby.